The present invention relates to a flip chip bonding land waving prevention pattern, which is, in particularly, provided on a layer next to flip chip bonding lands in a printed board in order to mount a flip chip surely.
Recently, as miniaturization of semiconductor chips has been advanced with the progress of semiconductor elements, most elements are not only small in size but also large in number of their terminals. Along with the advancement, when flip chips (bare chips) are mounted, they are often turned upside down so that electrodes come down. That is, the flip chips are face-down mounted. As a practical structure of the face-down mounting of a flip chip, there is generally adopted a structure in which a foot print is provided in a printed board correspondingly to bumps of the flip chip, and face-down mounting is performed between the bumps and the foot print. As for the method of mounting a semiconductor chip, bumps are bonded onto a plurality of electrodes of the semiconductor chip one by one by a capillary of a bonding device, and the semiconductor chip is pressed onto a glass substrate so as to level the height of the bumps.
On the other hand, pads corresponding to the electrodes of the semiconductor chip are formed by photolithography on a mounting surface of an FPC (Flexible Printed Circuitboard), and an thermosetting and insulating bonding agent is applied to the pads by screen printing. Then, the pads of the FPC and the bumps of the semiconductor chip are positioned on a bonding stage of the bonding device, and the semiconductor chip is pressed and heated by a bonding head so as to connect the pads with the bumps electrically, and so as to harden the thermosetting and insulating bonding agent, at the same time, to fix the semiconductor chip onto the FPC.
However, in such a face-down mounting structure of a flip chip, the pads and the bumps are connected with each other surely if the thickness of the FPC is uniform and the flatness among the pads is superior. But, if there is no pattern on a layer adjacent to and directly below the foot print, portions having a signal pattern 4 and portions having no signal pattern 4 are mixed as shown in FIG. 10, so that interlaminar thickness cannot be made uniform. In the portions having no signal pattern 4, flip bonding lands 1 become wavy so that they cannot be connected. Therefore, it has been proposed to provide a dummy pattern to make the flip bonding lands flat.
For example, in a structure for face-down mounting bumps of a flip chip on a printed-wiring board, as disclosed in JP-A-9-223715, a dummy pattern is provided in a position corresponding to the bumps of the flip chip and in a place having no pattern on a layer adjacent to and directly below a foot print. Sinking-down to the foot print side and/or scattering in deformation due to pressing and heating for melting and hardening a connection medium is hardly caused at the time of mounting so that the interlaminar board thickness is made uniform. Alternatively, a dummy pattern is disposed in all the positions corresponding to the bumps on a layer adjacent to and directly blow the foot print, or a dummy pattern is formed into a single-plane pattern corresponding to a plurality of foot prints and connected to a power supply or the ground.
On the other hand, in a method of mounting a semiconductor chip, as disclosed in JP-A-8-64927, a dummy pattern for compensating ununiformity in board thickness is formed before execution of a bonding process between pads of a circuit board and bumps of a semiconductor chip. When the dummy pattern for compensating ununiformity in board thickness is formed, the flatness among the pads of the circuit board is improved because the thickness of the circuit board can be made substantially uniform. Therefore, electric connection is accurately performed by the displacement of the bumps caused by pressing and heating when the semiconductor chip is mounted.
According to the background art, a dummy pattern was provided partially or all over the surface of a printed board. That is, since the dummy pattern was provided independently of the shape of a flip-chip, it was difficult to make uniform the thickness of the board in an area corresponding to the shape of the flip chip. Accordingly, it was impossible to satisfactorily prevent lands from waving.